A High-Fat Compared with a High-Carbohydrate Breakfast Enhances 24-Hour Fat Oxidation in Older Adults.

Background: The ability to oxidize fat is associated with a lower risk of chronic metabolic disease. Preclinical data in mice showed that a high-fat "breakfast" increased 24-h fat oxidation relative to a high-carbohydrate breakfast. Objectives: The objectives of this study were to determine whether the timing of macronutrient intake in humans affects daily fuel utilization and to examine associations between fuel utilization and metabolic indexes. Methods: Participants were 29 healthy sedentary men and women (aged 55-75 y) with a body mass index (kg/m2) between 25 and 35. Participants were randomly assigned to receive either a high-fat breakfast (FB; 35% carbohydrate, 20% protein, 45% fat; n = 13) or a high-carbohydrate breakfast (CB; 60% carbohydrate, 20% protein, 20% fat; n = 16) for 4 wk while consuming a "neutral" lunch and dinner. Twenty-four-hour and postprandial respiratory quotients (RQs) were measured by whole-room indirect calorimetry. Insulin and glucose measures including insulin sensitivity were determined by an oral-glucose-tolerance test. Measures were taken at baseline and after the 4-wk intervention. Group-by-time interactions were determined by 2-factor repeated-measures mixed-model ANOVA. Pearson's correlation analyses were used to determine associations of 24-h RQs with metabolic measures after the intervention. Results: There was a significant group-by-time interaction for change in the 24-h RQ [FB (mean ± SD): 0.88 ± 0.02 to 0.86 ± 0.02; CB: 0.88 ± 0.02 for both; P < 0.05], breakfast RQ (FB: 0.88 ± 0.03 to 0.86 ± 0.03; CB: 0.89 ± 0.02 to 0.90 ± 0.02; P < 0.01), and lunch RQ (FB: 0.089 ± 0.03 to 0.85 ± 0.03; CB: 0.89 ± 0.03 for both; P < 0.01). In the CB group at follow-up, 24-h RQ was positively associated with fasting glucose (r = 0.66, P < 0.05), glucose area under the curve (AUC) (r = 0.51, P < 0.05), and insulin AUC (r = 0.52, P < 0.05) and inversely associated with insulin sensitivity (r = -0.51, P < 0.05). Conclusions: The macronutrient composition of breakfast affects substrate utilization throughout the day in older adults. The consumption of a high-fat, lower-carbohydrate breakfast may reduce the risk of metabolic disease. This trial was registered at www.clinicaltrials.gov as NCT03164200.

Effects of a eucaloric reduced-carbohydrate diet on body composition and fat distribution in women with PCOS.

OBJECTIVE: To determine if consumption of a reduced-carbohydrate (CHO) diet would result in preferential loss of adipose tissue under eucaloric conditions, and whether changes in adiposity were associated with changes in postprandial insulin concentration. METHODS: In a crossover-diet intervention, 30 women with PCOS consumed a reduced-CHO diet (41:19:40% energy from CHO:protein:fat) for 8 weeks and a standard diet (55:18:27) for 8 weeks. Body composition by DXA and fat distribution by CT were assessed at baseline and following each diet phase. Insulin AUC was obtained from a solid meal test (SMT) during each diet phase. RESULTS: Participants lost 3.7% and 2.2% total fat following the reduced-CHO diet and STD diet, resp. (p<0.05 for difference between diets). The reduced-CHO diet induced a decrease in subcutaneous-abdominal, intra-abdominal, and thigh-intermuscular adipose tissue (-7.1%, -4.6%, and -11.5%, resp.), and the STD diet induced a decrease in total lean mass. Loss of fat mass following the reduced CHO diet arm was associated with lower insulin AUC (p<0.05) during the SMT. CONCLUSIONS: In women with PCOS, consumption of a diet lower in CHO resulted in preferential loss of fat mass from metabolically harmful adipose depots, whereas a diet high in CHO appeared to promote repartitioning of lean mass to fat mass.

Return of hunger following a relatively high carbohydrate breakfast is associated with earlier recorded glucose peak and nadir.

The aim of this study is to test the hypothesis that a breakfast meal with high carbohydrate/low fat results in an earlier increase in postprandial glucose and insulin, a greater decrease below baseline in postprandial glucose, and an earlier return of appetite, compared with a low carbohydrate/high fat meal. Overweight but otherwise healthy adults (n = 64) were maintained on one of two eucaloric diets: high carbohydrate/low fat (HC/LF; 55:27:18% kcals from carbohydrate:fat:protein) versus low carbohydrate/high fat (LC/HF; 43:39:18% kcals from carbohydrate:fat:protein). After 4 weeks of acclimation to the diets, participants underwent a meal test during which circulating glucose and insulin and self-reported hunger and fullness, were measured before and after consumption of breakfast from their assigned diets. The LC/HF meal resulted in a later time at the highest and lowest recorded glucose, higher glucose concentrations at 3 and 4 hours post meal, and lower insulin incremental area under the curve. Participants consuming the LC/HF meal reported lower appetite 3 and 4 hours following the meal, a response that was associated with the timing of the highest and lowest recorded glucose. Modest increases in meal carbohydrate content at the expense of fat content may facilitate weight gain over the long-term by contributing to an earlier rise and fall of postprandial glucose concentrations and an earlier return of appetite.

Effects of diet macronutrient composition on body composition and fat distribution during weight maintenance and weight loss.

OBJECTIVE: Qualitative aspects of diet may affect body composition and propensity for weight gain or loss. We tested the hypothesis that consumption of a relatively low glycemic load (GL) diet would reduce total and visceral adipose tissue under both eucaloric and hypocaloric conditions. DESIGN AND METHODS: Participants were 69 healthy overweight men and women. Body composition was assessed by DXA and fat distribution by CT scan at baseline, after 8 weeks of a eucaloric diet intervention, and after 8 weeks of a hypocaloric (1000 kcal/day deficit) diet intervention. Participants were provided all food for both phases, and randomized to either a low GL diet (<45 points per 1000 kcal; n = 40) or high GL diet (>75 points per 1000 kcal, n = 29). RESULTS: After the eucaloric phase, participants who consumed the low GL diet had 11% less intra-abdominal fat (IAAT) than those who consumed the high GL diet (P < 0.05, adjusted for total fat mass and baseline IAAT). Participants lost an average of 5.8 kg during the hypocaloric phase, with no differences in the amount of weight loss with diet assignment (P = 0.39). Following weight loss, participants who consumed the low GL diet had 4.4% less total fat mass than those who consumed the high GL diet (P < 0.05, adjusted for lean mass and baseline fat mass). CONCLUSIONS: Consumption of a relatively low GL diet may affect energy partitioning, both inducing reduction in IAAT independent of weight change, and enhancing loss of fat relative to lean mass during weight loss.

Associations of total and undercarboxylated osteocalcin with peripheral and hepatic insulin sensitivity and ß-cell function in overweight adults.

CONTEXT: Animal studies indicate that osteocalcin (OC), particularly the undercarboxylated isoform (unOC), affects insulin sensitivity and secretion, but definitive data from humans are lacking. OBJECTIVE: The objectives of the study were to determine whether total OC and unOC are independently associated with insulin sensitivity and ß-cell response in overweight/obese adults; whether glucose tolerance status affects these associations; and whether the associations are independent of bone formation, as reflected in procollagen type 1 amino propeptide (P1NP). DESIGN, SETTING, AND PARTICIPANTS: This was a cross-sectional study conducted at a university research center involving 63 overweight/obese adults with normal (n = 39) or impaired fasting glucose (IFG; n = 24). MAIN OUTCOME MEASURES: Serum concentrations of total/undercarboxylated OC and P1NP were assessed by RIA; insulin sensitivity was determined by iv glucose tolerance test (S(I)-IVGTT), liquid meal test (S(I) meal), and homeostasis model assessment of insulin resistance; ß-cell response to glucose [basal ß-cell response to glucose; dynamic ß-cell response to glucose; static ß-cell response to glucose; and total ß-cell response to glucose] was derived using C-peptide modeling of meal test data; and intraabdominal adipose tissue was measured using computed tomography scanning. RESULTS: Multiple linear regression, adjusting for intraabdominal adipose tissue and P1NP, revealed that total OC was positively associated with S(I)-iv glucose tolerance test (P < .01) in the total sample. OC was not associated with S(I) meal or homeostasis model assessment of insulin resistance. In participants with IFG, unOC was positively associated with static ß-cell response to glucose and total ß-cell response to glucose (P < .05), independent of insulin sensitivity. CONCLUSIONS: In overweight/obese individuals, total OC may be associated with skeletal muscle but not hepatic insulin sensitivity. unOC is uniquely associated with ß-cell function only in individuals with IFG. Further research is needed to probe the causal inference of these relationships and to determine whether indirect nutrient sensing pathways underlie these associations.

Favourable metabolic effects of a eucaloric lower-carbohydrate diet in women with PCOS.

OBJECTIVE: Diet-induced reduction in circulating insulin may be an attractive nonpharmacological treatment for women with polycystic ovary syndrome (PCOS) among whom elevated insulin may exacerbate symptoms by stimulating testosterone synthesis. This study was designed to determine whether a modest reduction in dietary carbohydrate (CHO) content affects ß-cell responsiveness, serum testosterone concentration and insulin sensitivity in women with PCOS. DESIGN: In a crossover design, two diets ('Standard,' STD, 55:18:27% energy from carbohydrate/protein/fat; lower-carbohydrate, 41:19:40) were provided for 8 weeks in random order with a 4-week washout between. PATIENTS: Thirty women with PCOS. MEASUREMENTS: ß-cell responsiveness assessed as the C-peptide response to glucose during a liquid meal test; insulin sensitivity from insulin and glucose values throughout the test; insulin resistance (HOMA-IR); and total testosterone by immunoassay. RESULTS: Paired t-test indicated that the lower-CHO diet induced significant decreases in basal ß-cell response (PhiB), fasting insulin, fasting glucose, HOMA-IR, total testosterone and all cholesterol measures, and significant increases in insulin sensitivity and dynamic ('first-phase') ß-cell response. The STD diet induced a decrease in HDL-C and an increase in the total cholesterol-to-HDL-C ratio. Across all data combined, the change in testosterone was positively associated with the changes in fasting insulin, PhiB and insulin AUC (P < 0·05). CONCLUSIONS: In women with PCOS, modest reduction in dietary CHO in the context of a weight-maintaining diet has numerous beneficial effects on the metabolic profile that may lead to a decrease in circulating testosterone.

Effects of habitual diet on ethnic differences in serum total ghrelin.

Ghrelin, an orexigenic hormone, may be involved in the etiology of obesity. African Americans (AA) experience higher obesity rates than European Americans (EA), but it is unclear whether ghrelin differs with ethnicity. This study was designed to compare ghrelin concentrations between overweight AA and EA adults in a post absorptive state, in response to a standard meal, and after 8-week habituation to diets of differing macronutrient profiles. Sixty-one overweight men and women (31 EA and 30 AA) were assigned to either a higher-carbohydrate/lower-fat diet (55% CHO, 18% PRO, 27% FAT) or a lower-carbohydrate/higher-fat diet (43% CHO, 18% PRO, 39% FAT) for 8 weeks. At baseline and week 8, participants ingested a standard liquid mixed meal. Blood was sampled before the meal and serially after ingestion to measure total ghrelin and insulin. Hunger was assessed with a visual analog scale. Composite scores for ghrelin, insulin, and hunger were calculated as area under the curve (AUC), and ghrelin suppression was calculated as the change from fasting concentration. Fasting ghrelin and ghrelin AUC were higher among EA at baseline and week 8 (p < 0.001), and these differences were not affected by diet habituation. Despite greater postprandial ghrelin suppression, EA displayed greater hunger immediately following the test meal (p < 0.05). Overweight EA displayed higher circulating ghrelin and greater ghrelin suppression compared to AA. Further study is warranted to explore the physiological basis for these ethnic differences and to determine whether they may relate to higher obesity rates among AA.

Circulating ghrelin and GLP-1 are not affected by habitual diet.

BACKGROUND: Ghrelin and glucagon-like peptide-1 (GLP-1) are gut hormones known to induce hunger and satiety, respectively. Current knowledge about the effects of different macronutrients on circulating ghrelin and GLP-1 comes mainly from acute test meals, whereas little is known about the effects of chronic dietary intake on gut hormone secretion. This study was designed to examine whether 8-week habituation to diets with different percentages of carbohydrate and fat would affect serum ghrelin, GLP-1, and subjective hunger in a postabsorptive state and in response to a standard liquid mixed meal. METHODS: Sixty-one overweight men and women were provided all food for 8 weeks of either a higher-carbohydrate/lower-fat diet (High-CHO/Low-FAT; 55% CHO, 18% PRO, 27% FAT) or a lower-carbohydrate/higher-fat diet (Low-CHO/High-FAT; 43% CHO, 18% PRO, 39% FAT). After overnight fasts at baseline and week 8, participants consumed a standard liquid meal (7 kcals/kg, 58.6% CHO, 17.4% PRO, 24% FAT). Blood was sampled before the meal and at 15, 60, 90, 120, 180, and 240 min to determine total serum ghrelin and active GLP-1. Hunger was assessed by a visual analog scale. Mixed models were used to evaluate whether the temporal patterns of total serum ghrelin and active GLP-1 differed with diet. RESULTS: Although both diet groups reported greater hunger after 8 weeks (p=0.03), circulating ghrelin and GLP-1 were not affected by acclimation to different macronutrients. CONCLUSION: Habituation to different diets does not appear to influence fasting ghrelin, fasting GLP-1, or responses of these gut hormones to a standard meal.

A higher-carbohydrate, lower-fat diet reduces fasting glucose concentration and improves ß-cell function in individuals with impaired fasting glucose.

The objective was to examine the effects of diet macronutrient composition on insulin sensitivity, fasting glucose, and ß-cell response to glucose. Participants were 42 normal glucose-tolerant (NGT; fasting glucose <100 mg/dL) and 27 impaired fasting glucose (IFG), healthy, overweight/obese (body mass index, 32.5 ± 4.2 kg/m(2)) men and women. For 8 weeks, participants were provided with eucaloric diets, either higher carbohydrate/lower fat (55% carbohydrate, 18% protein, 27% fat) or lower carbohydrate/higher fat (43:18:39). Insulin sensitivity and ß-cell response to glucose (basal, dynamic [PhiD], and static) were calculated by mathematical modeling using glucose, insulin, and C-peptide data obtained during a liquid meal tolerance test. After 8 weeks, NGT on the higher-carbohydrate/lower-fat diet had higher insulin sensitivity than NGT on the lower-carbohydrate/higher fat diet; this pattern was not observed among IFG. After 8 weeks, IFG on the higher-carbohydrate/lower-fat diet had lower fasting glucose and higher PhiD than IFG on the lower-carbohydrate/higher-fat diet; this pattern was not observed among NGT. Within IFG, fasting glucose at baseline and the change in fasting glucose over the intervention were inversely associated with baseline PhiD (-0.40, P < .05) and the change in PhiD (-0.42, P < .05), respectively. Eight weeks of a higher-carbohydrate/lower-fat diet resulted in higher insulin sensitivity in healthy, NGT, overweight/obese individuals, and lower fasting glucose and greater glucose-stimulated insulin secretion in individuals with IFG. If confirmed, these results may have an impact on dietary recommendations for overweight individuals with and without IFG.

Dietary macronutrient composition affects ß cell responsiveness but not insulin sensitivity.

BACKGROUND: Altering dietary carbohydrate or fat content may have chronic effects on insulin secretion and sensitivity, which may vary with individual metabolic phenotype. OBJECTIVE: The objective was to evaluate the contribution of tightly controlled diets differing in carbohydrate and fat content for 8 wk to insulin sensitivity and ß cell responsiveness and whether effects of diet would vary with race, free-living diet, or insulin response. DESIGN: Healthy overweight men and women (36 European Americans, 33 African Americans) were provided with food for 8 wk and received either a eucaloric standard diet (55% carbohydrate, 27% fat) or a eucaloric reduced-carbohydrate (RedCHO)/higher-fat diet (43% carbohydrate, 39% fat). Insulin sensitivity and ß cell responsiveness were assessed at baseline and 8 wk by using a liquid meal tolerance test. RESULTS: Insulin sensitivity did not change with diet (P = 0.1601). Static ß cell response to glucose (ФS) was 28.5% lower after the RedCHO/higher-fat diet. Subgroup analyses indicated that lower ФS with the RedCHO/higher-fat diet occurred primarily among African Americans. A significant inverse association was observed for change in glucose area under the curve compared with change in ФS. CONCLUSIONS: Consumption of a eucaloric 43% carbohydrate/39% fat diet for 8 wk resulted in down-regulation of ß cell responsiveness, which was influenced by baseline phenotypic characteristics. Further study is needed to probe the potential cause-and-effect relation between change in ФS and change in glucose tolerance. This trial is registered at clinicaltrials.gov as NCT00726908.

Associations of free fatty acids with insulin secretion and action among African-American and European-American girls and women.

Ethnic differences in insulin secretion and action between African Americans (AAs) and European Americans (EAs) may influence mobilization of free fatty acids (FFAs). We tested the hypotheses that FFA concentrations would be associated with measures of insulin secretion and action before and during a glucose challenge test. Subjects were 48 prepubertal girls, 60 premenopausal women, and 46 postmenopausal women. Fasting insulin (insulin(0)), the acute insulin response to glucose (AIR(g)), the insulin sensitivity index (S(I)), basal and nadir FFA (FFA(0), FFA(nadir)), and nadir time (TIME(nadir)) were determined during an intravenous glucose tolerance test (IVGTT). Stepwise multiple linear regression (MLR) analysis was conducted to identify associations of FFA(0), FFA(nadir), and TIME(nadir) with ethnicity, age group, insulin measures, indexes of body composition from dual-energy X-ray absorptiometry, and measures of fat distribution from computed tomography scan. In this population, insulin(0) and AIR(g) were higher among AAs vs. EAs, whereas S(I) was lower, independent of age group. MLR analyses indicated that FFA(0) was best predicted by lean tissue mass (LTM), leg fat mass, ethnicity (lower in AAs), S(I), and insulin(0). FFA(nadir) was best predicted by FFA(0), age group, and intra-abdominal adipose tissue (IAAT). TIME(nadir) was best predicted by leg fat mass, AIR(g), and S(I). In conclusion, indexes of insulin secretion and action were associated with FFA dynamics in healthy girls and women. Lower FFA(0) among AAs was independent of insulin(0) and S(I). Whether lower FFA(0) is associated with substrate oxidation or risk for obesity remains to be determined.

High-milk supplementation with healthy diet counseling does not affect weight loss but ameliorates insulin action compared with low-milk supplementation in overweight children.

Milk consumption has decreased in children over the past years. This may play a role in the prevalence of pediatric obesity, because clinical studies have found a beneficial effect of milk consumption for weight management. The objectives of this study were to test whether high-milk consumption leads to greater weight loss and improvements in metabolic risk factors than low milk consumption during a 16-wk healthy eating diet. Overweight children aged 8-10 y were randomized to either high (4 x 236 mL/d) or low (1 x 236 mL/d) milk consumption. Children were provided dietary counseling on healthy eating at baseline and at wk 1, 2, 4, 6, 8, and 12. Serum glucose, insulin, and lipids were measured in fasting children at baseline and wk 8 and 16. An oral glucose tolerance test and body composition assessment by magnetic resonance imaging were conducted at baseline and endpoint. Body weight changes during the 16-wk study not differ between the high-milk (1.3 +/- 0.3 kg) and low-milk (1.1 +/- 0.3 kg) groups. There was no beverage x week interaction on any of the body composition and metabolic variables studied (blood pressure, serum lipids, glucose, and insulin). There was a beverage x week interaction (P = 0.044) on insulin area under the curve showing a trend toward reduced insulin output with a glucose challenge after high-milk consumption (P = 0.062). These data suggest that in overweight children, high-milk consumption in conjunction with a healthy diet does not lead to greater weight loss but may ameliorate insulin action compared with low-milk consumption.

Medium chain triglyceride oil consumption as part of a weight loss diet does not lead to an adverse metabolic profile when compared to olive oil.

OBJECTIVE: Medium chain triglyceride (MCT) consumption may have a beneficial impact on weight management, however, some studies point to a negative impact of MCT oil consumption on cardiovascular disease risk. This study examined the effects of MCT oil consumption, as part of a weight loss diet, on metabolic risk profile compared to olive oil. DESIGN: Thirty-one men and women, age 19-50 y and body mass index 27-33 kg/m(2), completed this randomized, controlled, 16-week weight loss program. Oils were consumed at a level of approximately 12% of the subjects' prescribed energy intakes in the form of muffins and liquid oil. RESULTS: After controlling for body weight, there was a significant effect of time on fasting serum glucose (P = 0.0177) and total cholesterol (P = 0.0386) concentrations, and on diastolic blood pressure (P = 0.0413), with reductions in these variables occurring over time; there was no time-by-diet interaction for any of the parameters studied. Two of the 3 subjects in the MCT oil group with evidence of the metabolic syndrome at baseline did not have metabolic syndrome at endpoint. In the olive oil group, 6 subjects had the metabolic syndrome at baseline; 2 subjects no longer had metabolic syndrome at endpoint, 1 person developed metabolic syndrome, and 4 subjects did not have any change in their metabolic syndrome status. CONCLUSIONS: Our results suggest that MCT oil can be incorporated into a weight loss program without fear of adversely affecting metabolic risk factors. Distinction should be made regarding chain length when it comes to discussing the effects of saturated fats on metabolic risk factors.